Heretofore use has been made of bolt-on extension fingers which extend forwardly from the harvester comb of a grain harvesting machine, since under certain conditions which are sometimes encountered (for example, light, shatter prone and in some cases tangled crops) it is advantageous to assist guidance of the crop into the fingers which embody the cutter bar severing surfaces, thus reducing shatter and other losses. However there are some problems which are encountered in that metal finger extensions can sometimes be caused to bend or fracture and pass rearwardly into the harvester machine, and may smash some elements of that machine, for example the auger which is usually located rearwardly of the comb, or the thresher drum.